22 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



Occurrence. — Chester group, Kaskaskia, Illinois {D. kaskaskiensis) , 

 Polk County, Missouri (£. optatus), Huntsville, Alabama (Ste. Gene- 

 vieve limestone), and Grayson County and Sloans Valley, Kentucky 

 (Glen Dean). 



Plesiotypes.—U.S.NM. nos. S-3883, S-3884. 



ULRICHIDISCUS Bassler, 1935 



Ambulacra all curve strongly to the left with slightly imbricated 

 interambulacrals. Lebetodiscus has similar curvature, but the inter- 

 ambulacrals are mosaic. 



Genotype and only known species. — U. (Agelacrinus) pulaskiensis 

 (Miller and Gurley) from the Mississippian (Chester) of Kentucky. 



COOPERIDISCUS Bassler, 1935 



Theca and general characters as in Ulrichidisciis, but all the rays 

 curve to the right and are separated by closely imbricating interambu- 

 lacrals. Foerstediscus has a similar curvature, but the interam- 

 bulacrals are mosaic. 



Genotype and only knoivn species. — C. (Lepidodiscus) alleganius 

 (Clarke) from the Devonian (Chemung) of New York. 



Family EDRIOASTERIDAE Bather 



This family was founded on the character of the ambulacra, which 

 were so strongly developed that they passed on to the aboral surface. 

 However, this seems to be a minor feature since the dividing line 

 between the upper and lower surface may be questionable. The occur- 

 rence of the ambulacral flooring plates in two rows is a more definite 

 character. 



Illustrations of the genotype of Edrioaster Billings, 1858 (pi. i, 

 fig. i) and of Dinocystis Bather, 1898 (pi. i, figs. 2, 3), the latter 

 probably belonging to the family are introduced here for comparative 

 purposes. 



Family CYATHOCYSTIDAE Bassler 



In this family the number of rows of marginal plates has been 

 increased to such an extent that they form a solid, fused, more or 

 less cone-shaped mass attached at the aboral end to some foreign 

 object, and bearing the ambulacra at the top or free end. Two genera 

 have been distinguished, Cyathocystis Schmidt, 1880, with an oral 

 surface much as in Stromatocystites, and Cyathotheca Jaekel, 1927, 

 in which the ambulacral areas are apparently so narrow that they are 



